The present invention generally relates to an apparatus for a monopole phased array thermotherapy applicator employed in deep heating of cancerous, precancerous, or benign tumors or infected or diseased tissue, such as arthritic tissue and tissue involving the human immunodeficiency virus (HIV) in a patient""s body.
The most difficult aspect of administering thermotherapy to deep organs in the body is to provide sufficient heating of the deep organ without burning the skin. Methods for producing an adaptively focused electromagnetic energy beam at a deep tumor position have been described in U.S. Pat. Nos. 5,251,645, 5,441,532, 5,540,737, and 5,810,888, all of which are incorporated herein by reference.
U.S. Pat. No. 5,251,645 describes an adaptive RF hyperthermia phased array that uses feedback measurements from noninvasive electric field sensors to null or reduce undesirable temperature hot spots in healthy tissue, while focusing the array radiation on a tumor. U.S. Pat. No. 5,441,532 describes a monopole phased array applicator device used to heat deep seated tumors using RF or microwave focusing while simultaneously minimizing the occurrence of temperature hot spots by using adaptive nulling. U.S. Pat. No. 5,540,737 describes an adaptive monopole waveguide phased array on opposite sides of the compressed breast to heat deep seated tumors in the breast. U.S. Pat. No. 5,810,888 describes a monopole phased array for targeted drug delivery to tumors by adaptively heating and activating thermosensitive liposomes to release drugs into the tumor.
Deep tissue heating may result in burns to superficial tissues and as a result, it is particularly challenging to avoid burning superficial tissues while heating a deep tumor. Tumors that may require deep heating include those in the liver, lung, pancreas, ovaries, rectum, prostate, breast, and stomach. Further, regional heating is usually required as deep tumors are often advanced and therefore large in size. It is known in the art that radiofrequency (RF) hyperthermia for deep tumor treatments, in the range of about 43 to 46 degrees Celsius, is usually combined with either radiation therapy or chemotherapy for a synergistic effect. As developed in U.S. Pat. No. 5,810,888, thermotherapy can be also be used in adaptive phased array targeted drug delivery to selected tissues via thermosensitive liposomes, which are lipid bubbles containing a drug that is released at temperatures in the range of about 39 to 45 degrees Celsius. The assignee""s method may be used with a recently developed temperature sensitive liposome formulation with chemotherapy agents such as doxorubicin as described in U.S. Pat. No. 6,200,598 xe2x80x9cTemperature Sensitive Liposomal Formulation,xe2x80x9d Mar. 13, 2001 to Needham, in which drug agents are released at temperatures of approximately 39 to 45 degrees Celsius. Direct killing of cancerous tissue may be achieved with temperatures in the range of about 43 to 50 degrees Celsius. Specifically, cell kill may be induced by apoptosis in the range of about 43 to 45 degrees Celsius and by necrosis in the range of about 45 to 50 (or more) degrees Celsius (Gerhard et al., xe2x80x9cShort Term Hyperthermia: In Vitro Survival of Different Human Cell Lines After Short Exposure to Extreme Temperaturesxe2x80x9d, Cancer Therapy by Hyperthermia and Radiation, Streffer C, editor, Baltimore-Munich: Urban and Schwarzenberg. pages 201-203, 1978; and Harmon et al, xe2x80x9cCell Death Induced in a Murine Mastocytoma by 42-47xc2x0 C. Heating in vitro: Evidence that the Form of Death Changes From Apoptosis to Necrosis Above a Critical Heat Loadxe2x80x9d, Int J Radiat Biol vol. 58, pages 854-858, 1990). As direct killing of tissue cells may be achieved with temperatures in the range of 43 to 50 degrees Celsius, the challenge to avoid burning superficial tissues while heating the tumor still needs to be solved.
Thermotherapy at RF frequencies in the range of about 50 to 300 MHz with a large diameter ring array (about 1.5 to 3 times the diameter of the human body) is commonly suggested for deep tumor heating. A ring phased array composed of four waveguides with a coupling bolus for deep tumor heating was first introduced by von Hippel in 1973 (von Hippel et al., Dielectric Analysis of Bio-Materials, Massachusetts Institute of Technology, Laboratory for Insulation Research, Technical Report 13, pp. 16-19, AD-769 843). A dipole ring phased array concept for deep tumor heating has been described by Turner in U.S. Pat. No. 4,589,423, as well as in an article by Turner, P. F., Schaefermeyer, T., and Saxton, T. (Future Trends in Heating Technology of Deep-Seated Tumors, Recent Results in Cancer Research, vol. 107, pages 249-262, 1988).
One of the difficulties of treating patients with a large-diameter hyperthermia array without a waveguide enclosure is the requirement for a large water bolus to couple the RF energy in toward the body. The mass of the large water bolus resting on the patient""s body may be uncomfortable to the patient. A metallic shielded room often must enclose the hyperthermia apparatus due to stray radiation. Without a metallic waveguide enclosure, the array has the potential for stray RF energy radiating along the longitudinal axis of the patient creating potential comfort and safety concerns. Thus, a metallic shielded room is likely to be required to prevent stray RF energy from interfering with other electronic equipment in systems without a waveguide enclosure.
The above shortcomings are solved by the monopole phased array thermotherapy applicator according to the invention. The monopole phased array applicator radiates radiofrequency energy to induce a temperature rise in targeted tissue within a body and includes a plurality of monopole elements that each transmit electric-field radiation, a metallic waveguide with an RF reflecting ground plane surface with a plurality of circular holes for mounting the monopole elements, a waveform generator providing a source of electric field coupled to each monopole element through a respective phase and power weighting network, at least one electric field probe positioned on the skin surface of the patient""s body for detecting electric field radiation from the plurality of monopole elements, and a controller circuit coupled to the electric field probe that receives feedback signals to adjust the phase and power delivered to the plurality of monopole elements so that one or more adaptive nulls are formed on the surface of the body and a focus is formed at the target tissue to be treated.
An adaptive thermodynamic RF monopole phased array antenna applicator surrounds a target body and provides minimally invasive heating of tissue in the range of approximately 39 to 50 degrees Celsius. This applicator can be used for heat-alone treatment, to activate thermosensitive liposomes and preferentially deliver drugs to regions deep in the body, or it can be used synergistically with radiation therapy, chemotherapy, drugs, or gene therapy. The use of a monopole phased array permits focused heating of large tissue masses deep within the human body and, at the same time, provides patient comfort. When the array is operating in the adaptive phased array mode, the power and phase delivered to the phased array antenna elements are computer controlled using feedback signals measured by noninvasive electric-field and temperature sensors placed outside the body (e.g., on the patient""s skin and within the tissue region to be treated) to control a phase shifter and power amplifier network to adjust the phase and power delivered to the monopole elements to form one or more nulls on the patient""s skin surface, while focusing energy at a deep tissue site to heat the deep tissue site to the range of 39 to 46 degree Celsius. The magnitude of the nulls formed on the patient""s skin surface and the focus in the tissue treatment region may be controlled by an adaptive phased array fast acceleration gradient search computer algorithm that adjusts the phase and power delivered to the monopole elements. A fast acceleration adaptive nulling and focusing gradient search algorithm and monopole array applicator for deep tumor heating are disclosed in U.S. Pat. No. 5,810,888 to Fenn and can be used as a starting point.
Theoretically, the adaptive monopole phased array thermotherapy system is capable of clinically treating many different types of deep-seated tumors (cancerous and benign) such as those occurring in the prostate, breast, liver, rectum, colon, cervix, pancreas, stomach, bladder, lung, and other deep organ sites in the human body. This thermotherapy system can be used to target the delivery of drugs by heating the tissue and releasing drugs from thermosensitive liposomes circulating within the bloodstream in the vicinity of the targeted tissue. The same thermotherapy system can also be used in conjunction with target radiation thermotherapy to enhance the effectiveness of chemotherapy, drugs, and gene therapy.
In contrast with photodynamic therapy (Shum et al., Phototriggering of Liposomal Drug Delivery Systems, Advanced Drug Delivery Review, 2001, vol 53, pages 273-284.), which uses laser light to energize drugs or liposomal encapsulated drugs, deep heating with a noninvasive adaptive phased array thermotherapy system may be used to activate thermosensitive liposomes to concentrate a drug into a tumor and energize the drug. The word xe2x80x9cthermodynamicsxe2x80x9d refers to the physics of the relationship between heat and other forms of energy. The therapy described here can thus be referred to as an adaptive phased array (APA) thermodynamic therapy (TDT).